Metal films are used as diffusion barriers, anticorrosion surfaces, interconnects and resistors in microelectronics, reflective surfaces, antifriction and wear surfaces and decorative applications. They can be deposited by dip and powder coating methods, electrochemical and electroless depositions f...
In a van der Waals heterostructure of two-dimensional materials, electronic properties are tunable by means of stacking orders. Here, we study the spin-dependent quantum transport in the bilayer of ferromagnetic zigzag-edged graphene/hexagonal-$\mathrm{BN}$ nanoribbons (ZGr-BNNRs) using density-functional theory combined with the Keldysh nonequilibrium Green's-function method. We reveal a strong odd-even effect of transport across the ZGr-BNNRs and a giant magnetoresistance value observed only in even-width ZGr-BNNRs. More interestingly, this value can be optimized by engineering stacking orders, yielding the perfect spin polarization efficiency of 100% and the magnetoresistance value of over ${10}^{4}$ in even-width ZGr-BNNRs. Our results provide a route to design and fabricate high-performance spin filters and magnetic storage devices.
In this paper, fifteen kinds of metal contacts to monolayer MoS2 and WS2 are investigated by first principles calculations. In a variety of metal contacts, the sixth subgroup metals (including Cr, Mo, W) show collective advantages in forming contacts with MoS2 or WS2. They have more favorable interface bonding, higher densities of states at the Fermi level, and lower potential barriers. Molybdenum (Mo) is one of the elements that form molybdenum disulphide (MoS2), and has been proved to form high quality contacts with MoS2. Similarly, tungsten (W) is one of the elements that form tungsten tellurium (WTe2), and is suggested to form favorable contacts with WTe2. The third metal in the sixth subgroup, chromium (Cr), is found here to be a superior metal compared with molybdenum and tungsten to form favorable contacts with molybdenum disulphide and tungsten disulphide. In all sixth subgroup metal contacts, Cr/MoS2 and Cr/WS2 show the best electronic transport properties and chromium has a lower melting point than molybdenum and tungsten, which lead to easier to process devices with transition-metal dichalcogenides.
Using first-principles calculations, we investigate the photogalvanic effect (PGE) in photodetectors based on tungsten telluride/molybdenum telluride heterostructures. Our calculations reveal that the photocurrent generated by the PGE exhibits a highly asymmetric response along the armchair and zigzag directions, which is sensitive to the light polarization state and direction. Furthermore, a large photocurrent can be obtained for almost the entire visible range without the application of external source-drain voltage, thus avoiding the problem of dark current. The photocurrent in the armchair photodetector is significantly enhanced compared to that in a basic photodetector. It also exhibits a sinusoidal dependence on the polarization angle and chirality of the circular polarization in agreement with phenomenological models of the second-order photocurrent response to the electric field of the light. Furthermore, the photodetector shows a high sensitivity to the polarization direction with an extinction ratio greater than 140 in the armchair direction. These advantageous properties suggest that is a promising candidate material for photodetection applications.
Dissolved gas analysis (DGA) of transformer oil can deeply understand the operation status of oil-immersed transformers, and detect early transformer failures as early as possible, thus achieving the purpose of preventing further damage to the transformer. It is a highly reliable method for identifying early-stage faults in transformers. This paper reviews the commonly used sensing technologies for analyzing dissolved gases in transformer oil, including Raman spectroscopy (RS), fourier transform infrared spectroscopy (FTIR), tunable diode laser absorption spectroscopy (TDLAS) and photoacoustic spectroscopy (PAS). The progress of research on these four gas sensing technologies is reviewed, with a detailed analysis of their respective principles and characteristics. This work provides guidance for the selection of appropriate online gas preliminary sensing technology, which is essential for the assessment of transformer operating conditions to ensure the stable operation of power systems.
In the engineering application of power transformers, due to phenomena such as overheating and partial discharge, the transformer may have a fault. Acetylene is one of the important characteristic components when the transformer is failure. The acetylene detection is significant to the diagnosis and evaluation of transformer operational condition. Therefore, a fiber loop ring-down system is built to detect acetylene in this paper. The fiber collimators at both ends of the gas cell are adjusted to reduce the loss of the gas cell system. The absorption line at 1531.6nm of the acetylene molecule was selected and the response characteristics of the system to the concentration of trace acetylene gas were studied through experiment. The ring-down waveforms at different concentrations of acetylene are measured. After fitting the peak value of waveforms, the corresponding ring-down time can be calculated and the quantitative relationship between ring-down time and concentration is also studied based on the least square method. The results show that there is a good linear dependence between the ring-down time and the concentration. The research results provide a new method for the online detection of dissolved gases in the transformer oil.
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